The present invention relates to an alarm device for a battery forklift truck, and more particularly to a battery voltage drop alarm device for suitably alarming that the battery voltage has dropped to less than a specified voltage.
In battery forklift trucks, it is necessary to inform an operator of the truck that the battery should be charged when the battery voltage has dropped to less than a prescribed value, since the insufficient battery voltage causes the normal operation of the forklift truck to be failed.
In conventional battery voltage drop alarm devices, the battery voltage drop is always detected and is indicated by a voltmeter, so that the operator observes the voltage value thereof to determine whether battery charge is required or not, thereby to prevent the overdischarge of the battery.
However, in general, the voltage drop of the battery in the auxiliary operation of the forklift truck very largely depends upon the kind of auxiliary work and weight of the load, so that it is essentially unstable as compared with that in propulsive operation of the battery forklift truck.
The term "auxiliary operation" is used herein to mean operation for moving a load relative to the body of the truck (for example, an operation for raising a fork carriage, an operation for tilting or traversing a mast or an operation for effecting rotational movement of a load) and in contrast to propulsive operation for moving the truck as a whole.
Consequently, in such battery voltage drop alarm devices as described above, in spite of the fact that the battery charge is actually sufficient, that is, the battery voltage is larger than the prescribed value, the operator may misjudge that it is necessary to charge the battery again at the time of auxiliary operation by observing the voltage drop on the voltmeter. Therefore, there is great possibility that although it is not necessary to charge the battery, the operator would have to stop the work in order to charge it; this causes the loss of time and decrease in work efficiency.